Order parameter fluctuations in natural time and b-value variation before large earthquakes

TL;DR

This paper investigates how fluctuations in the order parameter, reflected by the b-value in earthquake data, increase before large earthquakes, influenced by both the process's variance and memory effects, supported by observations and models.

Contribution

It demonstrates that b-value fluctuations before large earthquakes are affected by both infinite variance and temporal correlations, combining observational data and simulations.

Findings

b-value decreases before large earthquakes

Order parameter fluctuations increase approaching the critical point

Both variance and memory influence self-similarity in seismicity

Abstract

Self-similarity may stem from two origins: the process' increments infinite variance and/or process' memory. The $b$-value of the Gutenberg-Richter law comes from the first origin. In the frame of natural time analysis of earthquake data, a fall of the b-value observed before large earthquakes reflects an increase of the order parameter fluctuations upon approaching the critical point (mainshock). The increase of these fluctuations, however, is also influenced from the second origin of self-similarity, i.e., temporal correlations between earthquake magnitudes. This is supported by observations and simulations of an earthquake model.